The invention relates to a process for introducing an optical cable, consisting of a tube and optical waveguides introduced therein, into solid ground with the aid of a laying unit.
DE-A1-41 15 907 discloses a cable-laying plough for laying cables in the ground, in particular in the ground under water. In this case, the blade of the cable-laying plough has arranged in front of it a rotating cutting wheel which, in addition, is made to vibrate vertically, with the result that hard objects located in the region of the trench which is to be excavated may thus also be broken up thereby. This cable-laying plough excavates relatively wide trenches by displacing the soil with the aid of the plough blade. Such machines are used, in particular, in coastal areas and under water using corresponding control devices. For laying operations in the ground, the material is usually removed over a width of from 60 to 100 cm and a cable-laying depth of approximately 70 cm, with the result that the outlay for the laying operation is relatively high.
Furthermore, DE-A1-30 01 226 discloses a line network for transmitting signals, the signals being passed through fibre-optic cables which are laid in a network of pipes or ducts of an existing supply system. In this case, however, fixed cable-laying routes are predetermined, and inlets and outlets for the cable which is to be laid have to be provided in a suitable manner therein.
Alternatively to this, use may also be made, over short distances, of so-called drilling or jetting processes in which a tube is introduced horizontally into the ground. The high outlay for laying machines and material is also disadvantageous here.
JP-A-61 107 306 discloses an optical waveguide which is provided with a metal tube in order to increase tensile strength. The optical waveguide is provided with a sheath of vinyl, nylon or urethane, these materials having elastic properties and thus protecting the optical waveguide mechanically against external influences. In order to increase the tensile strength, a metallic tube is also applied, loosely at first. Then the tubes are stretched and thus secured to the sheathed optical waveguide.
FR-A-2 677 137 discloses a repair method for optical cables which are composed of a tube and optical waveguides running therein. At the defective point, an adapted tubular element is inserted, to which the ends of the defective tube are connected again, the defective point being bypassed.
EP-A-0 553 1991-A discloses a repair method for conventional optical cables, two cable sleeves being used in which the connections are made between the optical waveguides by means of an intermediate cable element.
The object of the present invention is to provide a process for introducing an optical cable in which the outlay for the laying operation can be reduced, it also being intended that the outlay for the optical cable system used be coordinated with the laying method. The set object is achieved according to the invention, by a first process
of the type explained in the introduction, in that the optical cable used is a microcable or minicable having an external diameter of the tube of 2.0 to 10 mm, preferably 3.5 to 5.5 mm, the tube being homogeneous and pressurized-water-tight,
a laying channel with a width of 4.5 to 12 mm, preferably 7 mm, which is adapted to the diameter of the microcable or minicable, being introduced with the laying unit into the solid underlying laying surface,
the microcable or micro[sic]cable being introduced into the laying channel by means of a feed element and being held at a constant laying depth, the laying channel being filled with filling material using a filling device which is moved along after the insertion of the microcable or minicable.
The object which has been set is thus achieved in accordance with the invention planning to a second method of the type mentioned at the beginning in such a way that a microcable or minicable with an external diameter of the tube of 2.0 to 10 mm, preferably 3.5 to 5.5 mm is pressed into utility lines for sewerage, gas or water, which have been left open, using a laying unit.
The object which has been set is achieved according to the invention using a third method of the type mentioned at the beginning in that the optical cable used is a microcable or minicable with a diameter of the tube of 2.0 to 10 mm, preferably 3.5 to 5.5 mm, which is inserted into existing, active utility lines for sewerage gas or water using a laying unit.
A great advantage of the process according to the invention is that only a relatively short amount of time is taken for the laying operation, with the result that it is used particularly wherever long-term hold-ups are undesirable. This is the case, for example particularly when laying new or additional cables, when the laying operation has to be carried out in urban areas with heavy traffic. Blocking off or diverting is to be avoided as far as possible. The operations of cutting, laying and sealing the channel can take place directly one after the other, these operations expediently being carried out all in one go by a multipurpose machine. In this manner, the traffic disruption is barely greater than that caused by a road sweeper. There is also such a need, for example, when all the laid pipes, cable ducts or pipelines have already had cables laid in them, it then being possible to splice onto the newly laid cables without interruption. Tubular mini communication cables, which are referred to as microcables or minicables, are particularly suitable for this purpose. These newly laid minicables or microcables may preferably be connected to form a redundant overlay network.
According to the invention, such a minicable or microcable comprises a homogeneous and pressurized-water-tight tube of very small diameter of from 2.0 to 10 mm, preferably 2.2 to 5.5 mm. These tubes have a wall thickness of from 0.2 to 0.4 mm. The most favourable values as regards the buckling resistance are achieved with a wall thickness to an external diameter ratio of between 1/5 and 1/20, preferably approximately 1/10. The smallest internal diameter of the tube used is 1.8 mm. This tube may be produced from metal, for example from chromium-nickel-molybdenum (CrNiMo188) steel, aluminium alloys, copper or copper alloys or from plastic, for example with reinforcement inserts consisting of carbon fibres, glass fibres, or a sintered carbon-fibre structure. These tubes may be extruded, welded, folded or bonded longitudinally at the overlap. The optical waveguides are then introduced into the tube either after the empty tube has been laid or at the factory. The optical waveguides can be blown in or jetted in.
The tubular minicable can be introduced into solid ground by various types of process according to the invention:
1. The laying may be carried out by means of a laying machine which has a cutting wheel, with the aid of which a narrow laying channel having a width of from 4 to 12 mm, preferably 7 mm, and a depth of from 50 to 100 mm, preferably 70 mm, is cut in the ground, in particular in an existing roadway.
2. Such a minicable may also be forced into disused supply lines (wastewater, gas, water). Disused pipelines of utility companies are particularly suitable for a laying operation. They correspond largely with the supply network planning to be set up. Even if the disused pipes are in bad condition, it is possible to introduce the thin metal tubes of the minicable since they are pressed in in the longitudinal direction and pass through obstructions such as dirt, rust and the like. The minicable does not buckle in pipes since it is supported by the disused supply line. After leaving these pipelines, the laying operation may also be continued with the aid of other laying processes.
3. It is likewise possible for a minicable to be pushed into existing, active supply lines (wastewater, water). The function of the supply lines is barely impaired to any extent at all in this case. The tubular minicable is resistant to pressurized water, wastewater and corrosion. Gnawing by rodents can be ruled out due to the large wall thickness of the metal tube. It can be assumed that the optical-waveguide network which is to be installed corresponds with the existing supply network. Earthworks may thus be reduced to a minimum. Appropriate fittings which make it possible to lift the minicable out of the supply lines are to be provided at the appropriate locations.
4. Minicables may likewise be introduced into the ground by earth-displacement or jetting processes. In this case, first of all the tube of the minicable is introduced, as a mechanical protection, into the ground. Expediently, the fibre conductors, or very thin blown fibres, are subsequently blown or jetted in. In order to minimize the friction during the blowing-in operation, the tubes, which are produced without seams and are smooth on the inside, are coated with a plastic layer, e.g. PTFE. This layer is, for example, deposited from a PTFE suspension when the metal tube is heated correspondingly. Moreover, this layer protects against corrosion and soiling of the tube interior. Earth-displacement and pressing-in operations in which a drilling head with a bevel rotates constantly are known. If the drilling head does not rotate, the drilling body is deflected in accordance with the bevel. It is thus possible to bypass obstructions. A water jet at very high pressure may, for example, force away small stones. The tube cuts or jets its way through the ground and assists the advancement of the pressing-in process. Moreover, the water pressure can move a piston in the drilling body. The thrust-like movement of the drilling head then breaks through obstructions more easily and reduces the static friction during the drawing-in operation.
By elastic expansion of the tube, the wall friction with respect to the earth can be reduced further. For this purpose, an outlet valve would have to be provided at the end of the tube.
Using the tubular minicable according to the invention, then, results in particular advantages, as follows. The laying or introduction takes place with the aid of a hollow tube, which, as cable, is already provided with optical waveguides; however, it is also possible for the optical waveguides to be drawn in subsequently. Appropriate selection of the wall thickness ensures sufficient protection against mechanical loading, corrosion and gnawing by rodents. Moreover, the tube has a high stability to transverse compressive stress. For lengthening and thinning the tube, use may be made of methods, which are known per se, with cutting clamping rings or a crimping process. For lengthening a tube consisting of copper, connection by cold pressure welding is possible, for example. Otherwise, the tube can be processed like a normal installation pipe, these methods relating to bending, provision of fittings, branchings and inlets in sleeves. Also suitable for this purpose are cylindrical metal fittings into which the minicable can be introduced tightly. When the laying operation is taking place from the surface of the ground, the surface is only minimally broken up, which is particularly advantageous for laying operations in roads. Moreover, as a result of the rigidity, pulling and pushing the minicable is, possible and helpful in the laying operation. Due to the small diameter of such a minicable, the earth displacement is also particularly low, it being possible for the earth to be displaced when the cable is pressed or drawn into the surrounding earth.
A tubular microcable or minicable is particularly suitable for laying in a roadway or in footpaths since the roadway formation is barely broken up by the necessary channel. All that is necessary in order to ensure the safety of such a cable is a channel having a width of 4 to 12 mm and a depth of approximately 70 mm. In this case, the channels for receiving the cables should, as far as possible, only be provided on the sides of the road since stressing is at its lowest here. The channel which has been introduced is refilled after the introduction of the cable or of the tube and is sealed against the penetration of surface water. This sealing must not produce any cavities in which surface water can collect. The roadway surface can be restored in a simple manner. All that is required during repair work is that, when the road surface is cut away, the minicable or microcable which has already been laid is not damaged.
A laying operation using a microcable and the corresponding laying process according to the invention produces considerable reductions in the costs for the laying method, this resulting in a considerable reduction in the overall line-laying costs in the case of a new installation. Moreover, the operational reliability is increased by redundant routing. It is also advantageous that annular network structures with various connection possibilities can be formed from former rigid, star-shaped branching networks. A flexible, intelligent network design is obtained in this manner, it being possible for microcables to be switched in with the aid of optical switches. A pigtail ring with optical switching, in which optical fibres could be routed as far as the subscriber, would thus be possible. It is highly advantageous that subsequent laying operations in roads, footpaths, cycle paths, curbstones and the like are possible with a low degree of outlay. Consequently, a technical concept may be adapted in a simple manner to the wishes of the operator, it being possible to utilize the existing infrastructure (wayleaves, and pipes for wastewater, gas, district heat, etc.) It should also be noted here that, in comparison with the standard method, this method can save a large amount of time.
Various points should be noted when a laying channel is provided in an asphalt surface of a federal road which is made up of a top surface course of 4 cm, a binder course of approximately 8 cm and a base course of from 10 to 15 cm. The proportion of bitumen decreases towards the base course, but the coarse-grained fillers increase. However, the bitumen ensures the cohesion within the individual layers. During cutting as far as the asphalt base course, the laying channel is, then, dimensionally stable, with the result that no material caves in and the overall upper road structure remains intact. During cutting, it is not permitted to cut through the bitumen base course as far as the anti-frost layer of the substructure since this may result in weak points in the series of asphalt layers, which weak points could break up the layer formation and result in damage to the road within a short period of time. However, if the minicable is laid in a water-tight and frost-resistant manner, the soil mechanics are not influenced by this intervention. However, modern roads are frost-resistant since the crushed-stone substructure bears and absorbs loads. This discharges gravitational water into the earth or into drain pipes, and a sealed, intact surface course does not let in any surface water. Frost damage cannot therefore occur. This minimum laying-channel width and vibration-free cutting means that the mechanical structure of the road remains intact. Directly after the laying operation, the laying channel is closed off again in a frost-resistant manner by a hot-melting bitumen or by a fusible preformed bitumen filler.
However, very heavy traffic may result in additional consolidation and flow in the upper structure of the road (lane grooves, shoulder). It is thus recommended that the laying channel is foam-filled with a curable plastic around the minicable directly after the latter has been laid. After curing, the foam filling achieves a compressive stressability which is sufficient for further distributing the load of the carriageway surface uniformly. Cavities and interstices between the minicable and the laying channel are filled, without leaving any cavities which could receive any surface water which may penetrate and propagate this surface water along the minicable.
Vibrations due to the heavy traffic are absorbed by the foam filling and are not passed on to the minicable. Relatively small occurrences of the earth subsiding may also be compensated for by the elastic foam, with the result that such irregularities in the bitumen base course would not result in the failure of the minicable due to bending of the tube or fibre elongation.
For a minicable according to the invention, compressed-gas monitoring and monitoring with a liquid, for example, are also possible. The minicable may thus also be filled with a liquid which, in the case of the tube having a defect, escapes and resinifies under the action of air. This ensures a kind of xe2x80x9cself-healingxe2x80x9d.
Moreover, the minicable is interception-proof since the optical waveguides cannot be bent. The minicable is stable with respect to transverse forces, has a high tensile force, is compact and, on account of the small diameter, has a relatively low weight and little friction. The tube, which acts as the cable sheath, also assumes, at the same time, the tensile-force function of the otherwise customary central element. In this high-strength cable with very low expansion, there is no problem in respect of excess lengths when the minicable is drawn in and laid. This configuration gives a higher strength in comparison with a normal cable with a conventional plastic cable sheath, with the result that it is also possible to work with considerably larger drawing-in forces. Moreover, straightforward earthing is possible in the case of the metal embodiment. If use is made of a plurality of tubes which are insulated with respect to one another, the metal cross-section may also be used for supplying power to active components. By using metal tubes, it would also be possible for overhead cables to be of a considerably more straightforward construction. A supporting element (e.g. a messenger wire) could then be dispensed with since the metal tubes assume this function. In addition, such a minicable is pressurized-water-tight, gas-tight, forms a water vapour barrier and gives protection against the gnawing of rodents. Furthermore, it is fire-resistant, has excellent heat-dissipation properties and is resistant to aging and corrosion.
The flexibility of the minicable or of the tube can be improved by a grooved sheath.
Further developments of the invention are given in subclaims.